Small form factor high-resolution camera

ABSTRACT

A camera including a spherically curved photosensor and a lens system. Effective focal length f of the lens system is within about 20% of the radius of curvature of the photosensor. An image is formed by the lens system at a spherically curved image plane that substantially matches the concave surface of the photosensor. The camera is diffraction-limited with small spot size, allowing small pixels to be used in the photosensor. F/number may be 1.8 or less. The spherically curved image plane formed by the lens system at the photosensor follows f*θ image height law. Chief rays of the lens system are substantially normal to the concave surface of the photosensor. Total axial length of the camera may be 2.0 mm or less. The camera may be implemented in a small package size while still capturing sharp, high-resolution images, making the camera suitable for use in small devices.

BACKGROUND

1. Technical Field

This disclosure relates generally to camera systems, and morespecifically to high-resolution, small form factor camera systems.

2. Description of the Related Art

The advent of small, mobile multipurpose devices such as smartphones andtablet or pad devices has resulted in a need for high-resolution, smallform factor cameras for integration in the devices. However, due tolimitations of conventional camera technology, conventional smallcameras used in such devices tend to capture images at lower resolutionsand/or with lower image quality than can be achieved with larger, higherquality cameras. Note that conventional small cameras use planarphotosensors, and the image plane formed by the lens system at thephotosensor of such cameras follows conventional f*tan(θ) image heightlaw. Achieving higher resolution with small package size camerasrequires use of a photosensor with very small pixel size (e.g., <1.2microns) and a very good imaging lens system. However, achievableresolution using conventional lens systems for small cameras has notbeen sufficient for such small pixels due to factors such as thez-height constraint, limitations on achievable F/number, andmanufacturing constraints.

SUMMARY OF EMBODIMENTS

Embodiments of the present disclosure may provide a high-resolutioncamera in a small package size. A camera is described that includes aspherically curved photosensor and a lens system. In at least someembodiments, the effective focal length (f) of the lens system is withinabout 20% of the radius of curvature (RoC) of the photosensor. The lenssystem may include in-line lens elements that refract light from anobject field to form an image on the concave surface of the photosensor.In some embodiments, a first lens element refracts light from the objectfield through a stop to a second lens element, and the second lenselement refracts light received from the first lens element to form theimage of the object field at the surface of the photosensor. The imageis formed by the lens system at a spherically curved image plane thatsubstantially matches the concave surface of the photosensor. In atleast some embodiments, paraxial image height of the image formed on theconcave surface of the photosensor by the lens system is substantiallyequal to f*θ, where θ (theta) is the deflection angle of the lenssystem. Thus, the lens system is an f*θ lens system, and the sphericallycurved image plane formed by the lens system at the photosensor followsf*θ image height law. Chief rays of the lens system are substantiallynormal to the concave surface of the photosensor. In at least someembodiments, F/number of the lens system, determined by the effectivefocal length (f) of the lens system and the diameter D of the entrancepupil, may be 1.6.

In some embodiments, the lens system may further include a third lenselement, positioned between the first two lens elements and thephotosensor, with optical characteristics that correct for chromaticaberration of the first and second lens elements.

Optical characteristics of the lens system may provide very small rayfan spot size for all field heights at the image plane, as well as avery small spot size for all field heights. In addition, the lens systemis diffraction-limited over the entire photosensor. This allows a smallphotosensor with small pixel size (e.g., less than 1.2 microns, forexample 1.1 microns) to be used in the camera while still providingsharp, high-resolution images. In at least some embodiments, total axiallength of the camera may be 2.0 millimeters (mm) or less. Thus, thecamera may be implemented in a small package size while still capturingsharp, high-resolution images, making embodiments of the camera suitablefor use in small and/or mobile multipurpose devices such as cell phones,smartphones, pad or tablet computing devices, laptop, netbook, notebook,subnotebook, and ultrabook computers.

Images captured using the camera may include barrel distortion.Embodiments of the camera may include or leverage an implementation of adistortion correcting algorithm that may be applied to images capturedby the camera system to correct for barrel distortion. Any of variousalgorithms for correcting barrel distortion may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a camera including a lens system with three lenselements and a spherically curved photosensor, according to someembodiments.

FIG. 2 illustrates chief rays in a camera as illustrated in FIG. 1.

FIG. 3 illustrates the relationship between the radius of curvature ofthe spherically curved photosensor and the effective focal length of thelens system in a camera as illustrated in FIG. 1.

FIGS. 4A and 4B illustrate example values for various parameters of thelens system and photosensor of a camera as illustrated in FIG. 1.

FIG. 5 illustrates an alternative implementation of a camera thatincludes a lens system with two lens elements and a spherically curvedphotosensor, according to at least some embodiments.

FIG. 6 shows a three-dimensional oblique view of a spherically curvedphotosensor, according to at least some embodiments.

FIG. 7 illustrates barrel distortion and distortion correction in acamera as illustrated in FIG. 1.

FIG. 8 is a flowchart of a method for capturing images using a camera asillustrated in FIGS. 1 through 4B, according to at least someembodiments.

FIG. 9 is a flowchart of a method for capturing images using a camera asillustrated in FIG. 5, according to at least some embodiments.

FIG. 10 illustrates an example computer system that may be used inembodiments.

This specification includes references to “one embodiment” or “anembodiment.” The appearances of the phrases “in one embodiment” or “inan embodiment” do not necessarily refer to the same embodiment.Particular features, structures, or characteristics may be combined inany suitable manner consistent with this disclosure.

“Comprising.” This term is open-ended. As used in the appended claims,this term does not foreclose additional structure or steps. Consider aclaim that recites: “An apparatus comprising one or more processor units. . . . ” Such a claim does not foreclose the apparatus from includingadditional components (e.g., a network interface unit, graphicscircuitry, etc.).

“Configured To.” Various units, circuits, or other components may bedescribed or claimed as “configured to” perform a task or tasks. In suchcontexts, “configured to” is used to connote structure by indicatingthat the units/circuits/components include structure (e.g., circuitry)that performs those task or tasks during operation. As such, theunit/circuit/component can be said to be configured to perform the taskeven when the specified unit/circuit/component is not currentlyoperational (e.g., is not on). The units/circuits/components used withthe “configured to” language include hardware—for example, circuits,memory storing program instructions executable to implement theoperation, etc. Reciting that a unit/circuit/component is “configuredto” perform one or more tasks is expressly intended not to invoke 35U.S.C. §112, sixth paragraph, for that unit/circuit/component.Additionally, “configured to” can include generic structure (e.g.,generic circuitry) that is manipulated by software and/or firmware(e.g., an FPGA or a general-purpose processor executing software) tooperate in manner that is capable of performing the task(s) at issue.“Configure to” may also include adapting a manufacturing process (e.g.,a semiconductor fabrication facility) to fabricate devices (e.g.,integrated circuits) that are adapted to implement or perform one ormore tasks.

“First,” “Second,” etc. As used herein, these terms are used as labelsfor nouns that they precede, and do not imply any type of ordering(e.g., spatial, temporal, logical, etc.). For example, a buffer circuitmay be described herein as performing write operations for “first” and“second” values. The terms “first” and “second” do not necessarily implythat the first value must be written before the second value.

“Based On.” As used herein, this term is used to describe one or morefactors that affect a determination. This term does not forecloseadditional factors that may affect a determination. That is, adetermination may be solely based on those factors or based, at least inpart, on those factors. Consider the phrase “determine A based on B.”While in this case, B is a factor that affects the determination of A,such a phrase does not foreclose the determination of A from also beingbased on C. In other instances, A may be determined based solely on B.

DETAILED DESCRIPTION

Embodiments of a camera including a spherically curved photosensor and alens system are described. The lens system may include two in-line lenselements that refract light from an object field to form an image on theconcave surface of the photosensor. A stop may be located between thetwo lens elements. In at least some embodiments, F/number of the lenssystem, determined by the effective focal length (f) of the lens systemand the diameter D of the entrance pupil, may be 1.8 or less. As anexample, in some embodiments, F/number of the lens system may be 1.6. Afirst lens element refracts light from the object field through thestop, and a second lens element refracts light received from the firstlens element to form the image of the object field at the surface of thephotosensor. In at least some embodiments, the effective focal length(f) of the lens system is within about 20% of the radius of curvature ofthe photosensor. The image is formed by the lens system at a sphericallycurved image plane that substantially matches the concave surface of thephotosensor. In at least some embodiments, paraxial image height of theimage formed on the concave surface of the photosensor by the lenssystem is substantially equal to f*θ, where θ (theta) is the deflectionangle of the lens system. Chief rays of the lens system aresubstantially normal to the concave surface of the photosensor. Thespherically shaped photosensor surface helps to dramatically reduce thefield curvature of the lenses. Using a curved photosensor, the fieldcurvature does not need to be well corrected for an imaging system withlarge field of view.

In at least some embodiments, the lens system may further include athird lens element positioned between the first two lens elements andthe photosensor. A third lens element may be selected with opticalcharacteristics that correct for chromatic aberration of the first andsecond lens elements. In other words, the third lens element may be usedto make the lens system achromatic. For example, in some embodiments, athird lens element may be used that is composed of a transparentmaterial that has a lower Abbe number (also referred to as the V-numberor constringence) than the transparent material used in the first andsecond lens elements. In optics, the Abbe number of an opticallytransparent material is a measure of the material's dispersion(variation of refractive index with wavelength) in relation to therefractive index of the material. A lower Abbe number represents a moredispersive transparent material. The use of an appropriately designedthird lens element of a material with a low Abbe number may act tocorrect for chromatic aberration of the first two lens elements.

Optical characteristics of the lens system may provide very small rayfan spot size for all field heights at the image plane, as well as avery small spot size for all field heights. In addition, the lens systemis diffraction-limited over the entire photosensor. This allows aphotosensor with small pixel size (e.g., less than 1.2 microns, forexample 1.1 microns) to be used in the camera while still providingsharp, high-resolution images. In addition, the lens system may includeonly two lens elements in some embodiments, or three lens elements inembodiments where a third lens element is used to correct for chromaticaberration, which reduces the axial (or z) length of the lens system andcamera when compared to conventional lens systems for small cameras. Inat least some embodiments, total axial length of the camera may be 2.0millimeters (mm) or less. In some embodiments, total axial length of thecamera may be 1.95 mm or less. Width of the camera may be 2.0 mm orless. Thus, the camera may be implemented in a small package size whilestill capturing sharp, high-resolution images, making embodiments of thecamera suitable for use in small and/or mobile multipurpose devices suchas cell phones, smartphones, pad or tablet computing devices, laptop,netbook, notebook, subnotebook, and ultrabook computers, and so on. Notethat aspects of the lens system and photosensor may be scaled up or downto provide cameras with larger or smaller package sizes.

A tradeoff is made in the camera design as described herein in thatimaged captured by the spherically-curved photosensor include geometric(barrel) distortion. See FIG. 7 for a graphical illustration of barreldistortion in a captured image of an object field introduced by a camerasystem. At least some embodiments may include or leverage a distortioncorrecting algorithm that may be applied to images captured by thecamera system to correct for barrel distortion, as shown in FIG. 7. Anyof various image processing algorithms for correcting barrel distortionin digital images as known in the art may be used. Commercial or customimplementations of the image processing algorithms may be used invarious embodiments.

Embodiments of the camera system may, for example, be implemented as acamera in various multipurpose computing devices, including but notlimited to small and/or mobile devices such as cell phones, smartphones,pad or tablet computing devices, and laptop, netbook, notebook,subnotebook, and ultrabook computers. In addition, embodiments of thecamera system may be implemented as stand-alone digital cameras. Inaddition to still (single frame capture) camera applications,embodiments of the camera system may be adapted for use in video cameraapplications.

FIG. 1 illustrates a camera including a lens system with three lenselements and a spherically curved photosensor, according to someembodiments. Camera 100 may include a lens system 110 that acts as animaging lens for the camera, and a spherically curved photosensor 120onto which lens system 110 projects an image at a spherically curvedimage plane that substantially coincides with the concave surface of thephotosensor 120. Lens system 110 includes three lens elements: lenselements 112, 114, and 116.

Lens elements 112 and 114 may be referred to as a first lens element anda second lens element, respectively. In at least some embodiments, lenselements 112 and 114 are both biconvex lenses (also referred to asconvex or positive lenses) that refract light received from an objectfield in front of the camera 100 and act together to focus the lightrays at a spherically curved image (or focal) plane at focal length f ofthe lens system. In at least some embodiments, lens elements 112 and 114may be composed of a moldable glass material. However, other transparentmaterials may be used. Lens elements 112 and 114 may be, but are notnecessarily, composed of the same material.

In at least some embodiments, lens system 110 is a mid-aperture lenssystem. That is, the stop (aperture) is located between lens elements112 and 114, as shown in FIG. 1. Note that, in optics, chief rays arethe light rays that pass through the center of the stop, as shown inFIG. 2. In at least some embodiments, the aperture (entrance pupil) ofthe stop may be designed to provide a low F/number equal to or less than1.8 for lens system 110. In some embodiments, for example, F/number oflens system 110 may be 1.6 (f/1.6). In optics, the F/number is the ratioof the focal length f of the lens system to the diameter of the apertureD (f/D). For example, in some embodiments, lens system 110 may havefocal length f of approximately 1.2 mm. To achieve f/1.6 with f=1.2 mm,diameter D of the aperture would be approximately 0.75 mm. One ofordinary skill in the art will recognize that f and/or D may be scaledto produce f/1.6 for camera 110 or to provide other F/numbers for camera100.

Lens element 116 may be referred to as a third lens element. In at leastsome embodiments, lens element 116 is a meniscus lens (a lens with aconcave surface and a convex surface). The concave surface faces thefirst and second lens elements, and thus the front of the camera, andthe convex surface faces the photosensor 120. In at least someembodiments, lens element 116 is a negative meniscus lens. In a negativemeniscus lens, the radius of curvature of the concave surface is lessthan the radius of curvature of the convex surface, and thus the lens isthinner at the center (at the optical axis) than at the edges. In atleast some embodiments, lens element 116 may be composed of an injectionmolded plastic material. However, other transparent materials may beused. In at least some embodiments, lens element 116 may be composed ofa material that has an Abbe number approximately opposite of the Abbenumber of the material used in lens elements 112 and 114 to correct forchromatic aberration of lens elements 112 and 114, thus making lenssystem 110 achromatic.

Spherically curved photosensor 120 may be an integrated circuit (IC)technology chip or chips implemented according to any of various typesof photosensor technology. Examples of photosensor technology that maybe used are charge-coupled device (CCD) technology and complementarymetal-oxide-semiconductor (CMOS) technology. In at least someembodiments, pixel size of the photosensor 120 may be 1.2 microns orless, although larger pixel sizes may be used. In an example embodiment,pixel size of the photosensor 120 may be 1.1 microns. In an exampleembodiment, photosensor 120 may be manufactured according to a 1280×720pixel image format to capture 1 megapixel images. Other pixel formatsmay be used in embodiments, for example 5 megapixel or 10 megapixelformats. Note that the camera system 100 may need to be appropriatelyscaled to support the larger formats. FIG. 6 shows a three-dimensionaloblique view of an example spherically curved photosensor 120 accordingto at least some embodiments, and is not intended to be limiting. Notethat the photosensor 120 in this example is shaped like a slice off ahollow sphere. An array of light-capturing pixel elements is located onthe inner surface. The outer surface may include connectors, pins,and/or other components for coupling the photosensor 120 to othercomponents within a device such as busses or other ICs.

Referring again to FIG. 1, lens system 110 acts to form a sphericallycurved image plane at or near the concave surface of spherically curvedphotosensor 120. As shown in FIG. 1, particular groups of light rays arefocused by lens system 110 at particular image points on the imageplane. Example light rays are shown for three groups of light rays thatare focused at three example image points. For clarity, FIG. 2 shows theoptical paths of only the chief rays of the three groups of light raysshown in FIG. 1. Chief rays are the rays that pass through the center ofthe stop. Note that the light ray represented as a solid line in FIG. 2is the chief ray along the optical axis of the camera 100.

As shown in FIG. 3, to form a spherically curved image plane at or nearthe surface of photosensor 120, the radius of curvature (RoC) of thephotosensor 120 is selected to be close to the effective focal length fof lens system 110. Alternatively, focal length f of lens system 110 maybe selected to be close to the RoC of the photosensor 120 viaappropriate selection of lens elements. For example, in someembodiments, the RoC of the photosensor may be within 15% of f. In someembodiments, the RoC of the photosensor may be within 12% of f. In someembodiments, the RoC of the photosensor may be within 10% of f. In someembodiments, the RoC of the photosensor may be substantially equal to f.

Optical characteristics of the lens system 110 provide very small rayfan spot size for all field heights at the image plane. In addition, thelens system 110 is diffraction-limited over the entire imageplane/photosensor 120. Paraxial image height of the image formed on theconcave surface of the photosensor 120 by the lens system 110 issubstantially equal to f*θ, where θ (theta) is the deflection angle ofthe lens system 110. Chief rays of the lens system 110 (see FIG. 3) aresubstantially normal to the concave surface of the photosensor 120. Insome embodiments, for example, the maximum chief ray angle is below 2°for a half diagonal field of view above 30°. The point spread function(PSF) and modulation transfer function (MTF) of lens system 110 are veryuniform over the photosensor 120. For example, in some embodiments, thePSF Strehl ratio is above 0.94 everywhere over the photosensor 120. Notethat the Strehl ratio is the ratio of the actual PSF to the PSF of anideal, aberration-free lens. Note that a lens system is considered to bediffraction-limited if the Strehl ratio is above 0.85, so lens system110 is a diffraction-limited lens system. In addition, relativeillumination in lens system 110 is above 80% for a half-diagonal fieldof view above 30°.

Example Lens System and Photosensor Parameters

This section describes an example configuration for a camera 400, withexample values for various parameters of the lens system 410 andphotosensor 420 with reference to FIGS. 4A and 4B. These parametervalues may, for example, be specified to manufacture the lens elements412, 414, and 416 and of photosensor 420. Note that the example valuesare not intended to be limiting. Also note that the values can be scaledto produce larger or smaller cameras, and/or cameras with differentimage formats or sizes (e.g., 5 megapixel image cameras rather than 1megapixel image formats).

FIG. 4A shows an example camera 400 including lens system 410 andphotosensor 420, according to at least some embodiments. Lens systemincludes lens elements 412, 414, and 416, and a stop. Lens system 410 isa mid-aperture lens system, with the stop located between lens elements412 and 414. Lens elements 412 and 414 may be composed of a moldableglass material. Lens element 416 may be composed of an injection moldedplastic material. Optical characteristics of the material of which lenselement 416 is composed may be chosen to correct for chromaticaberration of lens elements 412 and 414.

The inner and outer surface of each of lens elements 412, 414, and 416are labeled with numbers in FIG. 4A; the numbers are used to referencerows in the Table shown in FIG. 4B. The outer surfaces of the lenselements are those facing the front of the camera 400; the innersurfaces of the lens elements are those facing the photosensor 410. Theouter and inner surfaces of lens element 412 are labeled 430 and 432,respectively. The outer and inner surfaces of lens element 414 arelabeled 440 and 442, respectively. The outer and inner surfaces of lenselement 416 are labeled 450 and 452, respectively.

FIG. 4B is a Table of values for parameters of surfaces of lens elements412, 414, and 416, photosensor 420, and the stop, according to someembodiments. The first column lists the optical surfaces in the camera400 according to the labels in FIG. 4A. The remaining columns showexample values for radius of curvature (RoC), thickness, conic constant,and 4^(th), 6^(th), 8^(th), and 10^(th) order aspheric coefficients forthe optical surfaces listed in column 1, where relevant. The valuesgiven in FIG. 4B are not intended to be limiting. One or more of theparameters for one or more of the surfaces may be given different valueswhile still providing similar performance. In particular, note that thevalues in FIG. 4B may be scaled up or down for larger or smallerimplementations of the camera 400. Also note that the RoC of the opticalsurfaces are shown as positive or negative. The sign of an RoC indicatesthat the curvature is positive or negative with respect to a camerareference point; all of the surfaces share the same reference point. Inthis case, the reference point is at the back of the camera 400 (thephotosensor 420 side).

Using the example parameter values given in the Table in FIG. 4B, thefollowing optical characteristics are obtained in the camera 400. Notethat these values are given by way of example, and are not intended tobe limiting. Similar or different optical characteristics may beobtained using variations of the parameter values in FIG. 4A.

The effective focal length (f) of lens system 410 is 1.205 mm. Effectivefocal length f of lens system 410 is the distance from the principleplane to the vertex of the image plane (i.e., at the vertex of thespherically curved surface of photosensor 420) along the optical axis.The RoC of the photosensor 420 is 1.364 mm. Thus, f in this example is@88.3% of the RoC of the photosensor, and the difference between f andRoC of the photosensor ((RoC−f)/RoC) is @11.7%.

F/number of lens system 410 is f/1.6. To achieve f/1.6, diameter D ofthe entrance pupil of lens system 410 is approximately 0.75 mm. Smalleror larger F/numbers may be achieved by varying D and/or f, and f/1.6 maybe achieved in a scaled-up or scaled-down camera 400 by appropriatelyscaling D and f. In some embodiments, the entrance pupil may beadjustable to give other values for D, and thus other F/numbers for thecamera.

Back focal length (BFL) of lens system 410 is 0.291 mm. Back focallength of a lens system is the distance from the vertex of the lastoptical surface of the lens system (in this case, surface 452 of lenselement 416) to the rear focal point at the vertex of the image plane(i.e., at the vertex of the spherically curved surface of photosensor420) along the optical axis.

The lens system 410 includes only three lens elements, with the thirdlens element used to correct for chromatic aberration. This allows theaxial (or z) length of the lens system 410 to be reduced when comparedto conventional lens systems used in small package size cameras. Totalaxial length of the camera 400 is approximately 1.95 mm, allowing thecamera to be implemented in a short front-to-back package size, makingthe camera 400 suitable for use in small and/or mobile devices. Width ofthe camera 400 may also be 2.0 mm or less. As previously noted, thecamera parameters may be scaled up or down which may result in longer orshorter axial lengths and thus larger or smaller package sizes for someimplementations of the camera 400.

The photosensor 420 may be a spherically curved image sensor comprisingan array of light-sensing pixel elements on the spherically curved innersurface. Photosensor 420 may be implemented according to any of varioustypes of photosensor technology. Examples of photosensor technology thatmay be used are charge-coupled device (CCD) technology and complementarymetal-oxide-semiconductor (CMOS) technology. In at least someembodiments, the photosensor 420 may provide a high-definition, 1280×720image format with a pixel size of 1.1 microns (μm). Lens system 410affects light entering the front of the camera from an object field toform a spherically curved image plane at or near the spherically curvedinner surface of photosensor 420.

Optical characteristics of the lens system 410 provide very small rayfan spot size for all field heights at the image plane/photosensor 420.In addition, the lens system 410 is diffraction-limited over the entireimage plane/photosensor 420. Paraxial image height of the image formedon the concave surface of the photosensor 420 by the lens system 410 issubstantially equal to f*θ, where θ (theta) is the deflection angle ofthe lens system 410. Thus, lens system 410 is an f*θ lens system, asopposed to a conventional f*tan(θ) lens system typically used incameras. Chief rays of the lens system 410 (see FIG. 3) aresubstantially normal to the spherically curved inner surface of thephotosensor 420. The maximum chief ray angle (CRA) is below 2° for ahalf diagonal field of view above 30°. This small CRA decreases sensorcolor crosstalk and increases sensor signal-to-noise ration (SNR). Inaddition, relative illumination in lens system 410 is above 80% for ahalf-diagonal field of view above 30°. The SNR at the edge of the imageis higher than in conventional miniature cameras.

The point spread function (PSF) and modulation transfer function (MTF)of lens system 410 are very uniform over the photosensor 120. Lenssystem 410 is diffraction-limited; the PSF Strehl ratio of lens system410 is above 0.94 everywhere over the photosensor 420.

The PSF (point-spread function) is an important and accurate metric usedto evaluate a lens system's optical performance. The Strehl ratio of thePSF indicates how high the PSF peak is compared to an aberration-freelens. A lens system is generally considered diffraction-limited if theStrehl ratio is above 0.85. Lens system 410 has a Strehl ratio above0.94 over the entire pixel sensor array of photosensor 420. Thus, lenssystem 410 is diffraction-limited. In addition, the modulation transferfunction (MTF) of lens system 410, a measure of resolution (imagesharpness) that the lens system is capable of, is very uniform over theentire field height. In addition, lens system 410 has a very small rayfan spot size for all field heights, and a very small spot size for allfield heights.

The optical characteristics of lens system 410 make it possible to uselens system 410 with very small pixel sizes on photosensor 420, forexample 1.2 micron, 1.1 micron, or even smaller pixel sizes, while stillproviding very sharp, high-resolution images. This ability toeffectively use small pixels on photosensor 420 allows the photosensor420 to be implemented that can capture sharp, high-resolution, 1megapixel or larger images in a very small camera 400 package.

The spherically curved image plane formed by lens system 410 atphotosensor 420 does not follow conventional f*tan(θ) image height law.Instead, lens system 410 is an f*θ lens system, and follows f*θ imageheight law. Lens system 410 introduces a small amount of opticaldistortion (less than 1%) if paraxial chief ray height is calculated asf*θ. However, with the conventional definition of distortion which hasparaxial chief ray height calculated as f*tan(θ), the distortion may beabout 20%. Specifically, lens system 410 and spherically curvedphotosensor 420 result in some amount (less than 20%) of monotonicallyincreasing barrel distortion in captured images (see FIG. 7).Embodiments may include or leverage a distortion correcting algorithmthat may be applied to images captured by the camera system 400 tocorrect for barrel distortion, as shown in FIG. 7. The monotonicallyincreasing barrel distortion in captured images makes distortioncorrection relatively straightforward, and the resultingdistortion-corrected images are very accurate.

Camera 400 may be used for any imaging system that requires highresolution, high sensitivity, high SNR and small axial (or z) length.The lens system 410 and photosensor 420 design of camera 400 allows thecamera 400 to be very small (e.g., 2 mm or less) in axial length andwidth, while providing sharp, high resolution, and fast image capture.Camera 400 may thus be implemented in a small package size while stillcapturing sharp, high-resolution images, making the camera suitable foruse as a still camera or video camera in small and/or mobilemultipurpose devices such as cell phones, smartphones, pad or tabletcomputing devices, laptop, netbook, notebook, subnotebook, and ultrabookcomputers, and so on.

FIG. 8 is a flowchart of a method for capturing images using a camera asillustrated in FIGS. 1 through 4B, according to at least someembodiments. As indicated at 800, light from an object field in front ofthe camera is received at a first lens element of the camera. Asindicated at 802, the first lens element refracts the light through astop to a second lens element. As indicated at 804, the light is thenrefracted by the second lens element to a third lens element thatcorrects for chromatic aberration. As indicated at 806, the light passesthrough the third lens element to form an image at a spherically curvedimage plane at or near the concave surface of a spherically curvedphotosensor. As indicated at 808, the image is captured by thephotosensor. As indicated at 810, a distortion correction algorithm maythen be applied to the captured image to correct for geometric (barrel)distortion. Note that applying the distortion correction algorithm maybe optional.

In at least some embodiments, the first and second lens elements areboth biconvex lenses that refract light received from an object field infront of the camera and that act together to focus the light rays at thespherically curved image (or focal) plane at focal length f of the lenssystem. In at least some embodiments, the third lens element is anegative meniscus lens. In at least some embodiments, the third lenselement is composed of a material with different optical characteristicsfrom the first two lens elements and acts to correct for chromaticaberration of the first two lens elements.

Alternative Embodiments

The camera as illustrated in FIGS. 1 through 4B may alternatively beimplemented with two in-line lens elements instead of three in-line lenselements by leaving out the third lens element 116 and 416 in FIGS. 1and 4A, respectively. The third lens element corrects for chromaticaberration, but otherwise does not have a significant effect on theimage plane formed by the lens system. The remaining elements (the firsttwo lens elements and the photosensor) may be appropriately adjusted toaccount for any differences in optical characteristics, if necessary.

FIG. 5 illustrates a camera 500 implemented without the third lenselement, according to at least some embodiments. Camera 500 may includea lens system 510 that acts as an imaging lens for the camera, and aspherically curved photosensor 520 onto which lens system 510 projectsan image at a spherically curved image plane that substantiallycoincides with the concave surface of the photosensor 520. Lens system510 includes two lens elements: lens elements 512 and 514. A stop islocated between lens elements 512 and 514. In some embodiments, lenselements 512 and 514, photosensor 520, and the stop may be similar oridentical to the corresponding lens element 412 and 414, photosensor420, and stop shown and described in FIGS. 4A and 4B. However, thecomponents of the camera 500 may be appropriately adjusted in spacing,size, optical characteristics, material, or other aspects to providenecessary or desired optical performance in camera 500.

FIG. 9 is a flowchart of a method for capturing images using a camera asillustrated in FIG. 5, according to at least some embodiments. Asindicated at 900, light from an object field in front of the camera isreceived at a first lens element of the camera. As indicated at 902, thefirst lens element refracts the light through a stop to a second lenselement. As indicated at 904, the light is then refracted by the secondlens element to form an image at a spherically curved image plane at ornear the concave surface of a spherically curved photosensor. Asindicated at 906, the image is captured by the photosensor. As indicatedat 908, a distortion correction algorithm may then be applied to thecaptured image to correct for geometric (barrel) distortion. Note thatapplying the distortion correction algorithm may be optional.

In at least some embodiments, the first and second lens elements areboth biconvex lenses that refract light received from an object field infront of the camera and that act together to focus the light rays at thespherically curved image (or focal) plane at focal length f of the lenssystem.

Distortion Correction

As noted above, images captured with a camera as illustrated in FIGS. 1through 5 may include barrel distortion. A distortion correctionalgorithm may be applied to the images to correct for the distortion.The distortion correction algorithm may be implemented in softwareand/or hardware in a device that includes the camera. An example deviceis shown as computer system 2000 in FIG. 10. In some embodiments, thecamera may include processor(s) and memory that store programinstructions for implementing a distortion correction algorithmspecifically designed to correct for the distortion in images capturedby the camera. For example, the camera may be implemented as astand-alone camera system that includes hardware and/or software thatcan correct for the distortion in captured images in-camera.Alternatively, the camera may be implemented as a stand-alone camera,and the captured images may be transferred via a wired or wirelessconnection to another device which performs distortion correction.

In at least some embodiments, the camera may be implemented as acomponent in a multipurpose device such as a smartphone, tablet or padcomputing device, laptop or notebook computing devices, desktopcomputer, and so on. In these implementations, the camera may includeprocessor(s) and memory that store program instructions for implementinga distortion correction algorithm, or alternatively the distortioncorrection algorithm may be implemented and executed by the host device.In the latter case, custom distortion correction software may beprovided with the camera, or alternatively general-purpose imageprocessing software capable of correcting barrel distortion in imagesmay be used.

Other Applications

In addition to imaging applications, the lens system design, for exampleas illustrated in FIGS. 1 through 5, may be used in illumination andprojection applications. In these applications, in place of thespherically curved photosensor, a device that includes the lens systemwould include a spherically curved light source, for example an array oflasers (e.g., vertical cavity surface emitting laser (VCSEL) technologylasers) or of light-emitting diodes (LEDs) arranged according to aspherically curved shape (see FIG. 6). Thus, the photosensor is replacedby a light source, and the object field becomes a projection field. Thelens system acts in reverse, refracting light received from the lightsource to project a pattern of light onto the projection field.

Example Computing Device

FIG. 10 illustrates an example computing device, referred to as computersystem 2000, that may include or host embodiments of the camera asillustrated in FIGS. 1 through 9. In addition, computer system 2000 mayimplement methods for controlling operations of the camera and/or forcorrecting distortion in images captured with the camera, as describedabove. In different embodiments, computer system 2000 may be any ofvarious types of devices, including, but not limited to, a personalcomputer system, desktop computer, laptop, notebook, tablet or paddevice, slate, or netbook computer, mainframe computer system, handheldcomputer, workstation, network computer, a camera, a set top box, amobile device, a wireless phone, a smartphone, a consumer device, videogame console, handheld video game device, application server, storagedevice, a television, a video recording device, a peripheral device suchas a switch, modem, router, or in general any type of computing orelectronic device.

In the illustrated embodiment, computer system 2000 includes one or moreprocessors 2010 coupled to a system memory 2020 via an input/output(I/O) interface 2030. Computer system 2000 further includes a networkinterface 2040 coupled to I/O interface 2030, and one or moreinput/output devices 2050, such as cursor control device 2060, keyboard2070, and display(s) 2080. Computer system 2000 may also include one ormore cameras 2090 as described above with respect to FIGS. 1 through 9,which may also be coupled to I/O interface 2030.

In various embodiments, computer system 2000 may be a uniprocessorsystem including one processor 2010, or a multiprocessor systemincluding several processors 2010 (e.g., two, four, eight, or anothersuitable number). Processors 2010 may be any suitable processor capableof executing instructions. For example, in various embodimentsprocessors 2010 may be general-purpose or embedded processorsimplementing any of a variety of instruction set architectures (ISAs),such as the x86, PowerPC, SPARC, or MIPS ISAs, or any other suitableISA. In multiprocessor systems, each of processors 2010 may commonly,but not necessarily, implement the same ISA.

System memory 2020 may be configured to store program instructions 2022and/or data 2032 accessible by processor 2010. In various embodiments,system memory 2020 may be implemented using any suitable memorytechnology, such as static random access memory (SRAM), synchronousdynamic RAM (SDRAM), nonvolatile/Flash-type memory, or any other type ofmemory. In the illustrated embodiment, program instructions 2022 may beconfigured to implement various interfaces, methods and/or data forcontrolling operations of camera 2090 and for capturing and processingimages with integrated camera 2090 or other methods or data, for exampleinterfaces and methods for capturing, displaying, processing, andstoring images captured with camera 2090. In some embodiments, programinstructions and/or data may be received, sent or stored upon differenttypes of computer-accessible media or on similar media separate fromsystem memory 2020 or computer system 2000.

In one embodiment, I/O interface 2030 may be configured to coordinateI/O traffic between processor 2010, system memory 2020, and anyperipheral devices in the device, including network interface 2040 orother peripheral interfaces, such as input/output devices 2050. In someembodiments, I/O interface 2030 may perform any necessary protocol,timing or other data transformations to convert data signals from onecomponent (e.g., system memory 2020) into a format suitable for use byanother component (e.g., processor 2010). In some embodiments, I/Ointerface 2030 may include support for devices attached through varioustypes of peripheral buses, such as a variant of the Peripheral ComponentInterconnect (PCI) bus standard or the Universal Serial Bus (USB)standard, for example. In some embodiments, the function of I/Ointerface 2030 may be split into two or more separate components, suchas a north bridge and a south bridge, for example. Also, in someembodiments some or all of the functionality of I/O interface 2030, suchas an interface to system memory 2020, may be incorporated directly intoprocessor 2010.

Network interface 2040 may be configured to allow data to be exchangedbetween computer system 2000 and other devices attached to a network2085 (e.g., carrier or agent devices) or between nodes of computersystem 2000. Network 2085 may in various embodiments include one or morenetworks including but not limited to Local Area Networks (LANs) (e.g.,an Ethernet or corporate network), Wide Area Networks (WANs) (e.g., theInternet), wireless data networks, some other electronic data network,or some combination thereof. In various embodiments, network interface2040 may support communication via wired or wireless general datanetworks, such as any suitable type of Ethernet network, for example;via telecommunications/telephony networks such as analog voice networksor digital fiber communications networks; via storage area networks suchas Fibre Channel SANs, or via any other suitable type of network and/orprotocol.

Input/output devices 2050 may, in some embodiments, include one or moredisplay terminals, keyboards, keypads, touchpads, scanning devices,voice or optical recognition devices, or any other devices suitable forentering or accessing data by computer system 2000. Multipleinput/output devices 2050 may be present in computer system 2000 or maybe distributed on various nodes of computer system 2000. In someembodiments, similar input/output devices may be separate from computersystem 2000 and may interact with one or more nodes of computer system2000 through a wired or wireless connection, such as over networkinterface 2040.

As shown in FIG. 10, memory 2020 may include program instructions 2022,which may be processor-executable to implement any element or action tosupport integrated camera 2090, including but not limited to distortioncorrection or other image processing software and interface software forcontrolling camera 2090. In at least some embodiments, images capturedby camera 2090 may be stored to memory 2020. In addition, metadata forimages captured by camera 2090 may be stored to memory 2020.

Those skilled in the art will appreciate that computer system 2000 ismerely illustrative and is not intended to limit the scope ofembodiments. In particular, the computer system and devices may includeany combination of hardware or software that can perform the indicatedfunctions, including computers, network devices, Internet appliances,PDAs, wireless phones, pagers, video or still cameras, etc. Computersystem 2000 may also be connected to other devices that are notillustrated, or instead may operate as a stand-alone system. Inaddition, the functionality provided by the illustrated components mayin some embodiments be combined in fewer components or distributed inadditional components. Similarly, in some embodiments, the functionalityof some of the illustrated components may not be provided and/or otheradditional functionality may be available.

Those skilled in the art will also appreciate that, while various itemsare illustrated as being stored in memory or on storage while beingused, these items or portions of them may be transferred between memoryand other storage devices for purposes of memory management and dataintegrity. Alternatively, in other embodiments some or all of thesoftware components may execute in memory on another device andcommunicate with the illustrated computer system 2000 via inter-computercommunication. Some or all of the system components or data structuresmay also be stored (e.g., as instructions or structured data) on acomputer-accessible medium or a portable article to be read by anappropriate drive, various examples of which are described above. Insome embodiments, instructions stored on a computer-accessible mediumseparate from computer system 2000 may be transmitted to computer system2000 via transmission media or signals such as electrical,electromagnetic, or digital signals, conveyed via a communication mediumsuch as a network and/or a wireless link. Various embodiments mayfurther include receiving, sending or storing instructions and/or dataimplemented in accordance with the foregoing description upon acomputer-accessible medium. Generally speaking, a computer-accessiblemedium may include a non-transitory, computer-readable storage medium ormemory medium such as magnetic or optical media, e.g., disk orDVD/CD-ROM, volatile or non-volatile media such as RAM (e.g. SDRAM, DDR,RDRAM, SRAM, etc.), ROM, etc. In some embodiments, a computer-accessiblemedium may include transmission media or signals such as electrical,electromagnetic, or digital signals, conveyed via a communication mediumsuch as network and/or a wireless link.

The methods described herein may be implemented in software, hardware,or a combination thereof, in different embodiments. In addition, theorder of the blocks of the methods may be changed, and various elementsmay be added, reordered, combined, omitted, modified, etc. Variousmodifications and changes may be made as would be obvious to a personskilled in the art having the benefit of this disclosure. The variousembodiments described herein are meant to be illustrative and notlimiting. Many variations, modifications, additions, and improvementsare possible. Accordingly, plural instances may be provided forcomponents described herein as a single instance. Boundaries betweenvarious components, operations and data stores are somewhat arbitrary,and particular operations are illustrated in the context of specificillustrative configurations. Other allocations of functionality areenvisioned and may fall within the scope of claims that follow. Finally,structures and functionality presented as discrete components in theexemplary configurations may be implemented as a combined structure orcomponent. These and other variations, modifications, additions, andimprovements may fall within the scope of embodiments as defined in theclaims that follow.

What is claimed is:
 1. A camera, comprising: a spherically curvedphotosensor configured to capture light projected onto a concave surfaceof the photosensor; and a lens system configured to refract light froman object field located in front of the camera to form an image of thescene at a spherically curved image plane proximate to the concavesurface of the photosensor; wherein effective focal length f of the lenssystem is within 20% of the radius of curvature of the photosensor,wherein the lens system is diffraction-limited over the entire imageplane, and wherein chief rays of the lens system are substantiallynormal to the concave surface of the photosensor.
 2. The camera asrecited in claim 1, wherein F/number of the lens system is 1.8 or less.3. The camera as recited in claim 1, wherein F/number of the lens systemis 1.6.
 4. The camera as recited in claim 1, wherein paraxial imageheight of the image formed on the concave surface of the photosensor bythe lens system is substantially equal to f*θ, where θ is the deflectionangle of the lens system.
 5. The camera as recited in claim 1, whereintotal axial length of the camera is 2.0 millimeters or less.
 6. Thecamera as recited in claim 1, wherein the lens system comprises: a firstlens element and a second lens element; and a stop positioned betweenthe first and second lens elements; wherein the first lens element isconfigured to refract the light from the object field through the stopto the second lens element; and wherein the second lens element isconfigured to refract the light received from the first lens element toform the image of the scene at the spherically curved image planeproximate to the concave surface of the photosensor.
 7. The camera asrecited in claim 6, wherein the first and second lens elements arebiconvex lenses.
 8. The camera as recited in claim 6, wherein the lenssystem further comprises a third lens element positioned between thesecond lens element and the photosensor and configured to correct forchromatic aberration of the first and second lens elements.
 9. Thecamera as recited in claim 6, wherein the third lens element is anegative meniscus lens.
 10. The camera as recited in claim 1, whereinpixel size of the photosensor is 1.2 microns or less.
 11. The camera asrecited in claim 1, wherein the photosensor comprises an array of pixelelements on the concave surface operable to capture images of at leastone megapixel resolution.
 12. The camera as recited in claim 1, whereinthe camera further comprises a component configured to correct forgeometric distortion in images captured with the photosensor.
 13. Adevice, comprising: one or more processors; one or more cameras eachcomprising: a spherically curved photosensor configured to capture lightprojected onto a concave surface of the photosensor, wherein pixel sizeof the photosensor is 1.2 microns or less; and a diffraction-limitedlens system configured to refract light from an object field located infront of the camera to form an image of the scene at a sphericallycurved image plane proximate to the concave surface of the photosensor,wherein F/number of the lens system is 1.8 or less; wherein total axiallength of the camera is 2.0 millimeters or less; and a memory comprisingprogram instructions executable by at least one of the one or moreprocessors to control operations of the camera.
 14. The device asrecited in claim 13, wherein the program instructions are furtherexecutable by at least one of the one or more processors to correct forgeometric distortion in images captured by the one or more cameras. 15.The device as recited in claim 13, wherein the lens system comprises: afirst lens element configured to refract the light from the object fieldthrough a stop; and a second lens element configured to refract thelight received from the first lens element to form the image of thescene at the spherically curved image plane proximate to the concavesurface of the photosensor.
 16. The device as recited in claim 13,wherein the lens system further comprises a third lens elementpositioned between the second lens element and the photosensor andconfigured to correct for chromatic aberration of the first and secondlens elements.
 17. The device as recited in claim 13, wherein thephotosensor of each of the one or more cameras comprises an array ofpixel elements on the concave surface operable to capture images of atleast one megapixel resolution.
 18. A method for capturing images,comprising: receiving light from an object field in front of a camera ata first lens element of the camera, wherein the first lens element is abiconvex lens; refracting light from the first lens element through astop to a second lens element, wherein the second lens element is abiconvex lens; refracting light from the second lens element to form animage at a spherically curved image plane at or near a concave surfaceof a spherically curved photosensor; and capturing the image at theconcave surface of the spherically curved photosensor.
 19. The method asrecited in claim 18, wherein said refracting light from the second lenselement to form an image at a spherically curved image plane at or neara concave surface of a spherically curved photosensor comprises:refracting light from the second lens element to a third lens element,wherein the third lens element is a negative meniscus lens with opticalcharacteristics that correct for chromatic aberration of the first andsecond lens elements; passing light from the third lens element to formthe image at the spherically curved image plane at or near the concavesurface of the spherically curved photosensor.
 20. The method as recitedin claim 18, further comprising applying a distortion correctionalgorithm to the captured image to correct for geometric distortion inthe image.